Bacterial cells have evolved multiple regulatory mechanisms to ensure that their subcellular structures and organelles, such as pili and flagella, are assembled and positioned correctly. Our goal is to determine how the core components of a conserved regulatory system, and their interactions, have been adapted to serve the particular needs of different organisms. In Caulobacter crescentus, the protein components of this regulatory system (PodJ, DivJ, and PleC) follow defined patterns of subcellular localization that contribute to asymmetric cell morphology: organelles specifically develop at one pole but not the other. The regulatory components are conserved in Sinorhizobium meliloti, a related bacterium that induces nodule formation in plant roots during symbiosis. However, S. meliloti cells are morphologically symmetric compared to C. crescentus. We will examine how these conserved components function in S. meliloti to regulate the assembly of surface organelles and how this regulation affects host-microbe interaction. (1) We will first determine the localization patterns of the regulatory proteins and the phenotypes of null mutants that lack the proteins. (2) We will then detect and analyze changes in the mutants'transcriptional profiles to see if the proteins control expression of similar genes in different species. (3) We will also assess whether the mutations disrupt interaction between the bacterium and its hosts, preventing effective nodulation. In addition to these research objectives, the principal investigator aims to achieve the following developmental objectives under the guidance of a senior scientist: (4) establish an independent research group, (5) enhance mentoring skills, and (6) improve the quality of research. Relevance to Public Health: The proposed research is expected to reveal the driving principles of a regulatory pathway that exists in multiple bacterial species, including pathogens. Components of the pathway may serve as targets for new antimicrobial compounds.